Social animals benefit from sharing information that promotes fitness and survival. For example, there is extensive evidence that rodents can transmit dietary preferences to neonates and to peer conspecifics via chemosensory cues (Galef 2012). In many cases, this transmission of food preferences requires active social investigation by naïve “observers” of “demonstrators” that have consumed particular foods. Rats and mice will acquire food preferences from the breath of live conspecifics but fail to acquire preferences to food odors presented on the hind quarters of the other animal (Galef 1985). In contrast, “observer” rats are able to form preferences when allowed to smell, but not contact, anesthetized demonstrator rats dusted with odored foods (Galef 1985). Therefore, the social transmission of food preference requires concurrent detection of both social odors (such as those present in the breath of the demonstrator animal) and odors from a particular food source (eaten by the demonstrator) (Galef et al. 1983; Posadas-Andrews and Roper 1983; Galef and Kennett 1987; Galef et al. 1988; Galef 2012).
Rodents also exhibit a preference for food sources that are in close proximity to conspecific social odors such as those present in soiled nest materials (Pastro and Banks 2006; Galef 2012). Rats consistently prefer to eat from a food marked by the excretory products of conspecifics than from an unmarked alternative (Galef and Heiber 1976; Laland and Plotkin 1991), with urine markings and the presence of fecal deposits around a food site rendering these food sites attractive (Laland and Plotkin 1993). Together, this suggests that rodents find such feeding environments to be beneficial for survival. These benefits could include information about the quantity or quality of nearby food even after conspecifics have vacated the area, and would thus offer a useful parallel to information transmitted via more direct social interactions.
There is strong experimental support for a role of the olfactory system in the detection of the social cues necessary for the formation of socially-transmitted food preferences (Galef 2012). Carbon disulfide (CS2), an odorous component of rodent breath, can promote the acquisition of food preferences in both rats and mice when paired with a food odor (Bean et al. 1988; Galef et al. 1988; Munger et al. 2010). For example, rats will form food preferences when presented with cotton surrogates to which food odors and 1 ppm (13 μM) CS2 has been added, but will exhibit no preference when the surrogate is supplemented with food odor alone (Galef et al. 1988). This concentration of CS2 specifically activates a specialized subpopulation of olfactory sensory neurons (OSNs) in mice that express the receptor guanylyl cyclase isoform GC-D (Munger et al. 2010). Perturbation of the sensory transduction cascade in GC-D−expressing (GC-D+) OSNs, such as with the deletion of the gene encoding GC-D (Gucy2d), disrupts olfactory responses to CS2 and prevents mice from acquiring socially transmitted food preferences (Munger et al. 2010).
The discovery of social cues that can be more easily utilized than components of rodent breath might aid in the development of effective means for controlling populations of pest rodents. The present invention is directed to this and other important goals.